title: Interdigitated lamella and bicontinuous cubic phases formation from natural cyclic surfactin and its linear derivative.
abstract: The lyotropic phase behavior of the cyclic form surfactin (CS) produced by Bacillus subtilis and its linear derivative in aqueous solution was evaluated for the first time by using polarized light microscopy and small-angle X-ray scattering (SAXS). By polarized light microscopy, the aqueous solutions of CS at the concentrations above 50 wt% were optically anisotropic and gave mosaic textures, suggesting the formation of lamella structures, while those of the linear surfactin (LS) were optically isotropic and no distinctive textures were observed. SAXS diffractograms of the CS solution above 50 wt% clearly gave the three peaks whose spacing ratio of 1: 2: 3, indicating the presence of the lamellar (L(α)) phase, while those of the LS solution gave multiple peaks whose spacing ratios of √2: √3: √4: √6: √8, confirming the bicontinuous cubic (V₂) phase of the symmetry Pn3m. It was also found that the lamellar phase with CS was composed of not ordinary bilayer but interdigitated bilayer with the unusual packing of the acyl chain region. These results clearly demonstrated that the cyclic peptide structure plays a key role in regulating their self-assembly, and naturally occurring CS is likely to form lamellar structure by balancing bulky peptide headgroups with interdigitated packing of their acyl chains.
authors.affiliation: Research Institute for Innovation in Sustainable Chemistry, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8565, Japan. t-imura@aist.go.jp
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Imura
authors.forename: Shintaro
authors.initials: S
authors.lastname: Ikeda
authors.forename: Kenichi
authors.initials: K
authors.lastname: Aburai
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Taira
authors.forename: Dai
authors.initials: D
authors.lastname: Kitamoto
mesh_terms: D001412:Bacillus subtilis / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry*; D055666:Lipopeptides / Q000737:chemistry*; D010456:Peptides, Cyclic / Q000737:chemistry*; D012542:Scattering, Radiation
chemical_list: D001426:Bacterial Proteins; D055666:Lipopeptides; D010456:Peptides, Cyclic; C009365:surfactin peptide